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ss74nova

Serf 5 HP running problems

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ss74nova

Serf 5 HP running problems1968 Serf 990418 Briggs 5 HP 130902 0173-01 6804026 Seems to bog down under load. Can't set low idle, stalls under quarter throttle. New spark plug & gapped to .030, new points gapped to .020 & new condenser, new head gasket & torqued to 140 inlbs progressively according to briggs book, rebuilt carb, new governor spring, cleaned fuel tank, adjusted carb high speed mixture & no load speed to 3750 RPM, adjusted governor according to book & article from Al Eden. The low speed idle adjustment screw isn't even close to adjustment. It was this way before the carb rebuild too.What am I missing? If compression was low I don't think I would be able to pull start it. When hot or cold I have to pull start on choke twice then switch to full throttle & pull 2 or 3 times before it starts. It was this way also before carb rebuild.Could I have the wrong carb to governor rod? Any ideas? Thanks.Here's some pics of the carb. 1st pic is engine off throttle on stop.2nd pic is engine off throttle on low.3rd pic is engine off throttle on high.

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ss74nova

I didn't notice anything when I had it off, but I'll check again in a little while. The governor linkages seem free from the engine to carb when I manually move them & spring back to it's original position.

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steve-wis

Might be a valve issue, I would check the clearances on them. I assume when you did the head gasket that the valves looked ok and there wasn't any carbon on the sealing faces, or anything holding the intake slightly open. The other thing I would check is for an air leak where it might be sucking air. I don't see a primer bulb on that carb but if it has one check it for small cracks also.

Steve

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Bill725

If there is no gas filter, then maybe dirt/debris in the gas tank, If so, then I suggest pulling carb to clean, drain & clean out gas tank & install a fuel filter between the gas tank & carb. If the gas line is short, you can use the short B&S fuel filter.

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BLT
quote:Originally posted by BLT

Is there anything under the blower housing obstructing the air vane?


id="quote">
id="quote">Doh, I forgot. That carb has two suction pipes in the tank, a long one that almost goes to the bottom of the tank which delivers fuel to a well that is picked up by a second shorter pipe that finds its way to the carb. Both pipes have a fine mesh filter. Starts on page `13 or so in this manual. http://www.liberatedmanuals.com/TM-5-4240-501-14-and-P.pdf

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ss74nova

I pulled the blower housing & flywheel & found the wire from the coil to points got cut. Repaired & rerouted it, but still has problems.

Started right up with choke on cold start. Seems harder to start when hot. Doesn't start well with full throttle when hot, had to use half throttle or choke. When running on full throttle no load it sounds sluggish. I got the high speed mixture screw adjust to the smoothest running sound. As soon as a load is put on, it stalls. Still can't adjust low idle either.

When I rebuilt the carb I cleaned the tank & replaced both tubes with the mesh filters.

I sprayed brake clean around the carb & gas tank, & by the oring where the carb slides on the tube. No change in rpm.

Valves seemed ok. Didn't notice carbon build up. I didn't check valve clearances though. When I first got this tractor it wouldn't start. I sprayed rust penetrant in the spark plug hole with the valves open. It started after that & seem to run ok. Maybe there is a valve problem.

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ss74nova

Valve clearance intake is .004 & exhaust I can't even get a .0025 in there.

Put piston on top dead center & rotate past till piston is 1/4" below deck. Valve clearance specs are intake .005-.007 exhaust .009-.011.

I'm going to take the valves out & clean. Any ideas why they are below spec?

What to do after I clean the valves & seats? Should they be lapped? Should I replace the valve springs? I'm green in this area.

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steve-wis

As the valves wear, the clearances get smaller because the valve sets deeper into the seat. I would clean them, then check them for contact with the seat. You do this by putting a very small touch of bluing on the valve, sliding it down and against the seat without springs, and then rotate back and forth. Remove the valve and see if it is hitting all the way around. If it is, just grind the valve stem to remove the right amount of material to bring them into specs. This is a touchy process and it is very east to take off too much, so go very slowly and try to grind the valve stems nice and square. I usually try to get to the wider part of the tolerance, but if they are in the range it should work fine. Unless there is obvious damage to the springs, I usually don't replace them unless I do a complete overhaul.

Steve

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ss74nova

I checked the valve face contact areas.

The intake valve looks fine so I think I can just grind or sand the end down until the clearance is good.

The exhaust valve doesn't look so good. I put some gear paint on that you use for setting automotive gears up. A lot of it was left on the valve after I spun the valve.

The intake valve cleaned a spot off nicely all the way around the valve.

Should the exhaust valve be lapped in or something else. Never did this before. I know I shouldn't get valve grinding compound inside the engine. I have a valve lapping tool & grinding compound. What to do next? Thanks.

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steve-wis

I would run the piston to the bottom of the stroke and pack the cylinder with a rag. Also pack the pocket that the valve springs go in as well as you can while allowing the valve stem to enter. Use lapping compound and work at it until you have a decently wide land that the valve and seat contact on. You may need to grind the valve stem a bit before lapping so that the valve firmly contacts the seat. After you are done, a clean rag wet with paint thinner should wipe all the excess grit off. Remove the rags and again carefully wipe everything down with another clean rag. Finally, finish grind the valve stem to achieve the clearance needed.

Steve

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ss74nova
quote:Originally posted by BLT

You say new points meaning the f/w had to come off. Was re-torqued or hand tightened down?


id="quote">
id="quote">Thanks Bob.I guess thinking more about it I could have put a socket or crow's foot on the square for the recoil start & torqued it that way. That wouldn't hurt the ball bearings in the recoil start would it? If I do that I'm going to replace the key in the keyway also. Just to make sure it has the correct key & no slop.

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BLT

I have the clutch tools for installing and removing. I would think that If you lift cover off the clutch and you have at least four bearings to engage to spread the load, I would take a flyer on that. At least you can get a torq reading.

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ss74nova

I got the intake valve clearance in spec at .007. I was working on the exhaust valve & noticed a lot more slop or rocking back & forth between the stem & valve guide, like the exhaust guide is worn more.

Never noticed it smoking. What would be some symptoms of worn valve guides? Could this be part of my low power problem? Should I just put it back together & run it?

I don't have any briggs special tools. Is there a way to measure valve guides for wear without special briggs tools?

Thanks.

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ss74nova

Thanks guys for all your help. I had two problems just like both of you said.

I pulled the flywheel to replace the key, even though the old one seemed ok. I figured while I was there I would check the points again. Good thing I did, the gap was larger at .024. The PO had lost the old condenser hold down & made a homemade one. It must not kept enough pressure & vibrated loose. I fixed & modified it & put back together & torqed the flywheel to 65 ft lbs.

I lapped the exhaust valve & made sure I cleaned all the valve grinding compound out of the engine. Sanded the valve stem ends down to get the valve clearance with 240 grit wet/dry paper sprayed with WD-40 on a flat granite plate. Also worked good for the head to get it flat again. I couldn't get a .002 feeler guage between the head & straight edge when I was done.

Put all back together & fired it up. Set the high speed mixture. When I turned the screw in it would run rough, but when I turned it out it didn't run rough to notice even when I turned it out a whole turn from that point. I just backed it off 1/2 to 3/4 turn from the lean rough point. I was able to adjust it before. Seemed to run good though. I set the high & low speed idle. I'm able to adjust the low speed idle now!

I wanted to put a load on it with the mower, but the belt kept flying off. I drove it around in low range without the mower engaged & it seemed fine up hills & all over. My hi/lo won't work in high, so I wasn't able to run it in hi range. I'll look into that later.

The mower belt flies off when I disengage the mower. I think I got it adjusted right (1/4" gap) according to the manual.

How many belt stops are on it? There's one on each of the idlers on the deck. There's a wire one in front of the crank pulleys. I also have one on the left mule drive idler which goes on the top side of the belt behind the mule drive idler. Is this the correct location? Are there suppose to be two of them, one on the other mule drive idler also? I only saw one on the parts illustration.

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steve-wis

My mule drive only has one belt stop, but I have seen them with two, one on each side. I think the belt comes off when you disengage because it is backing off the mule drive too much. It might be the belt is stretched a bit. Mine has a metal flat plate on the mule drive that hits on the back side when you disengage the mower. It is slotted for adjustment. You might have to adjust this so the mule drive doesn't back off so far when you disengage. Otherwise, a new belt might be needed.

There is a great thread on the hi-lo units here. Do a search for it, I think Timflury started it. It will show the insides, and all the things you will need to check it out.

Steve

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ss74nova

NOS Simplicity belt. It flies off the right mule drive idler & the crank pulley. I'll take another look & see what I can do. I don't remember seeing a metal flat plate, but I'll look again.

Thanks!

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